1. Technical Field
The present invention relates to tissue piercing members and to trocar assemblies which incorporate such tissue piercing members.
2. Description of the Related Art
Trocar assemblies are well known devices for piercing body walls so as to gain access to underlying structures. In the context of minimally invasive surgical and diagnostic procedures, e.g., laparoscopic, thoracoscopic and arthroscopic procedures, the trocar is utilized to facilitate introduction of a cannula or guide sleeve through the body wall. The cannula, once positioned, provides a port of entry for additional instrumentation, e.g., an endoscope, clip applier, scissors, graspers, retractors, and the like. Recently, the development of essential mechanical instrumentation for use through cannulae has enabled the widespread acceptance of numerous minimally invasive procedures.
In introducing the initial trocar/cannula assembly through the body wall, the surgeon generally has no visualization of the body cavity or the location of internal structures. To provide an increased margin of safety, trocars have been developed which provide mechanisms adapted to cover the piercing member upon entry into the body cavity, e.g., SU 921554 to Markelov, U.S. Pat. No. 4,601,710 to Moll et al. and U.S. Pat. No. 5,116,353 to Green.
In utilizing trocar/cannula assemblies, the surgeon's control during entry is at least in part predicated on the penetration force required to pass the trocar through the body wall. The lower the force required, the more control the surgeon will have during entry. Thus, for example, U.S. Pat. No. 4,654,030 to Moll et al. provides a safety shielded trocar in which the safety shield is designed to minimize the trocar's penetration force. A variety of trocar piercing tip designs have also been disclosed, e.g., pyramidal and conical tips. U.S. Pat. No. 1,380,447 to Westcott discloses a trocar which includes a perforator or blade having a sharp tapered point and two sharp cutting edges. See also U.S. Pat. No. 4,499,898 to Knepshield et al. (surgical knife with controllably extendable blade), U.S. Pat. No. 3,584,624 to de Clutiis (catheter which receives rigid stylet with a cutting edge), U.S. Pat. No. 4,414,974 to Dotson et al. (microsurgical knife), U.S. Pat. No. 5,232,440 to Wilk (assembly for draining abscesses) and U.K. 1,356,386 to Moss et al. (artery entry tool). The design of the trocar's piercing tip will also influence the degree to which tissue is traumatized during trocar entry.
A need thus exists for a piercing tip design which maximizes the surgeon's control during trocar entry by reducing penetration force and which minimizes tissue trauma.